Optical disk drive capable of higher-speed seeking

ABSTRACT

An optical disk drive has a rough actuator for moving an optical head with respect to an optical disk and a fine actuator for moving an object lens with respect to the optical head, to transfer an optical spot from a present address to a target address. The optical disk drive controls the radial speed of an optical spot based on a trapezoidal speed profile. A deceleration period is effected when the remaining track number is at a threshold value. During the deceleration period when a rough actuator moves the optical head, fine actuator is moved in the direction opposite to the moving direction of the optical head to generate a stationary state of the optical spot. An address detector is activated during the stationary state to read the present address, thereby correcting the remaining track number. When the rough actuator is stopped, the seeking operation is completed without an additional fine seeking operation.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an optical disk drive capable ofhigher-speed seeking and, more particularly, to an optical disk drivecapable of higher-speed seeking by controlling a fine actuator during adeceleration period of a rough actuator.

(b) Description of the Related Art

Optical disk drives for driving a compact disk (CD) or a compact diskread-only memory (CD-ROM) has an optical head irradiating an opticalspot on a rotating disk file on which each data track includes data pitsfor read-out. The optical head detects the levels of intensity of areflected light from the data pits, thereby reading data recorded on thedisk file.

In CD drives or CD-ROM drives (hereinafter, simply referred to as CDdrives), since the recording density of the optical disk file as viewedalong a data track is constant over the whole track area in spite ofradial position of the data track on the optical disk file, the linearspeed of the disk file must be maintained constant by changing therotational speed thereof depending on the radial position of the datatrack. The linear speed data for respective tracks are stored beforehandin the CD drives. The CD drives calculate the number of tracks to becrossed during a seeking operation based on the linear speed data storedbeforehand, the address data of the present location (present address),on which the optical spot stays, and the address data of the targettrack (target address) included in the access command. The CD drivesthen move the optical spot to the target address based on thecalculation.

FIG. 1 shows a seeking process effected by a conventional optical diskdrive. After the optical disk drive receives an access command in stepS43, the optical disk drive reads out the present address Tp in stepS44. Subsequently, the optical disk drive first calculates radialposition r₁ of the present address Tp as viewed from the disk center, byusing the following equation: ##EQU1## wherein r_(o), tp and V_(L) areradial position of the minimum address from which the data is stored,the track pitch of the disk file and the linear speed at the presentaddress, respectively. Thereafter, radial position r₂ of the targetaddress Tt also calculated by using the following equation: ##EQU2##wherein V_(L) is the linear speed at the target track. Based on theresults, the number Nt of the tracks (cross-track number Nt) disposedbetween the present address before seeking and the target address isobtained in step S45 by using the following equation: ##EQU3## Theoptical disk drive then moves the optical head based on the cross-tracknumber Nt in a rough seeking operation, which is shown by steps S46 toS56. The rough seeking operation is effected based on a speed profile,such as shown in FIG. 2, including a first, acceleration period betweent0 and t1, a second, constant speed period between t1 and t2 and athird, deceleration period between t2 and t3. In short, the roughseeking operation is controlled based on a so-called trapezoid speedprofile.

During the acceleration period, the travelling speed of the optical headis raised up to a maximum speed Vmax, which is not higher than thecritical speed below which the tracking error signal can be detected.After the maximum speed Vmax is obtained at time instant t1, the maximumspeed Vmax is maintained, then deceleration period begins at the radialposition where the number of the remaining tracks to be crossedhereinafter, i.e., remaining track number is at a threshold value, attime instant t2. The movement of the optical head is finished at theposition where the remaining track number is zero at time instant t3.

In detail, after the remaining track number becomes a threshold valueNd, the speed V of the optical head for the deceleration period iscalculated by using the cross-track number Nt and the count Nc of thecrossed tracks (crossed-track count Nc) in step S51 as follows: ##EQU4##After the remaining track number Nt-Nc becomes zero at step S53, therough actuator is stopped in step S55, then the tracking servo system isactivated to read the present address data to finish the rough seekingoperation in step S56.

In the conventional method, however, the location at which the roughseeking operation is finished often deviates from the target track dueto errors in results of calculation of the linear speed or in thetracking error signal. Accordingly, read-out of the present address anda fine seeking operation follow the rough seeking operation. In detail,as shown in FIG. 3, one seeking operation includes the steps ofreceiving an access command (step S57), rough seeking (step S58),read-out of the present address (step S59), fine seeking (step S60),additional read-out of the present address (step S61) and awaiting diskrotation (step S63). The read-out can be executed by activating thetracking servo system during a stationary state of the optical spot. Thefine seeking operation is effected to position the optical spot exactlyat the target address and thereby requests the read-out of the presentaddress before the fine seeking and a subsequent calculation of a secondcross-track number in step S59.

In the conventional method, as described above, there is a limit forobtaining a higher-speed seeking to thereby reduce the access time forthe optical spot because of a number of the sequential steps of roughseeking, read-out of present address, fine seeking etc.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide an improved optical disk drive capable of reducing access timeof the optical spot.

In accordance with the present invention, there is provided an opticaldisk drive comprising an optical head for reading optical data storedalong a plurality of tracks of a disk file, a first actuator for movingthe optical head with respect to the disk file in a radial directionthereof, an object lens, mounted on the optical head, for irradiating anoptical spot onto the disk file, a second actuator, mounted on theoptical head, for moving the object lens with respect to the opticalhead in the radial direction, a speed sensor for detecting a radialspeed of the optical spot with respect to the disk file, an addressdetector for detecting a present address of the optical spot withrespect to the disk file, the second actuator moving the object lens inthe direction opposite to the moving direction of the optical head forcontrolling the radial speed of the optical spot to thereby generate astationary state of the optical spot with respect to the disk file, theaddress detector being activated to read a present address during thestationary state of the optical spot.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, features and advantages of the presentinvention will be more apparent from the following description,referring to the accompanying drawings in which:

FIG. 1 is a flowchart showing a seeking process for a rough seekingeffected by a conventional optical disk drive;

FIG. 2 is a graph showing a speed profile of the optical spot during therough seeking of FIG. 1;

FIG. 3 is a flowchart showing one seeking operation in the conventionaloptical disk drive;

FIG. 4 is a block diagram of an example of an optical disk driveaccording to the present invention;

FIG. 5 is a first part of a flowchart for a seeking process effected bythe optical disk drive of FIG. 3, showing a first embodiment of thepresent invention;

FIG. 6 is a remaining part of the flowchart of FIG. 5;

FIG. 7 is a graph for showing a speed profile obtained by the seekingoperation of FIGS. 5 and 6;

FIG. 8 is a graph for showing detailed speed profiles effected by arough actuator and a fine actuator;

FIG. 9 is a first part of a flow chart for showing a second embodimentof the present invention similarly to FIG. 5;

FIG. 10 is a remaining part of a flow chart of FIG. 9; and

FIG. 11 is a graph for showing detailed speed profiles effected by arough actuator and a fine actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments of the present invention will be described withreference to the drawings.

Referring to FIG. 4, an example of an optical disk drive according tothe present invention includes an optical head 4 for reading data storedin an optical disk file 14 rotatably mounted on a spindle motor 13, atracking control system for positioning an optical spot onto a targettrack of the optical disk file 14, and a reproducing section (not shownin the drawing) for processing data read-out by the optical head. Theoptical spot is irradiated from an object lens 4A movably mounted on theoptical head 4.

The tracking control system includes a rough actuator (first actuator) 2for moving the optical head 4 in a radial direction of the optical diskfile, a fine actuator (second actuator) 3 for moving the object lens 4Awith respect to the optical head 4 in the radial direction, a signaldetecting section 10 for generating a tracking error signal "a" based onthe data read-out by the optical head 4 from the disk file 14, a firstand a second phase compensating sections 11 and 12 each for compensatingthe tracking error signal "a" in the phase thereof to generate a drivingsignal for a corresponding one of the actuators 2 and 3, a codingsection 7 for coding the tracking error signal "a" supplied from thesignal detecting section 10, a first drive section 5 for driving thefine actuator 3 based on the output of the first phase compensatingsection 11, a second drive section 6 for driving the rough actuator 6based on the output of the second phase compensating section 12, across-track counter 8 for counting pulses of the coded cross-tracksignal "b" supplied from the coding section 7 to thereby generate acrossed-track count, a speed detecting section or speed sensor 9 fordetecting the travelling speed of the optical spot based on the pulserepetition interval of the coded tracking error signal "b", and acontrol section 1 for controlling the first and second drive sections 5and 6 based on the travel distance supplied from the cross-track counter8 and the travelling speed supplied from the speed detecting section 9.

In general, the term "fine actuator" includes an object lens actuatorfor moving an object lens with respect to an optical head in thevertical direction of the disk file and a tracking servo actuator formoving the object lens with respect to the optical head in the radialdirection of the disk file. In this text, however, the fine actuator 3is defined as a tracking servo actuator for a simplification purpose.

The rough actuator 2 generally for a long distance use moves the opticalhead 4 with respect to the disk file, while the fine actuator 3generally for a small distance use moves the object lens 4A with respectto the optical head 4. The cross-track counter 8 is reset by the controlsection 1 before the optical spot moves or before the counting of thecrossed tracks is started.

FIGS. 5 and 6 as combined show a flowchart of a seeking process effectedby an optical disk drive according to a first embodiment of the presentinvention such as shown in FIG. 1. After the control section 1 receivesan access command including a target address data in step S17, thecontrol section 1 reads out in step S18 the present address Tp of thelocation on which the optical spots stays. Subsequently, the number Ntof tracks to be crossed during seeking travel from the present addressto the target address, i.e., initial cross-track number Nt is calculatedin step S19. The control section 1 then controls the first drive section5 based on the initial cross-track number Nt to drive the rough actuator2, thereby moving the optical head 4 in a radial direction in step S20.The control section 1 resets the crossed-track count in the cross-trackcounter 8, which starts to count up crossed-tracks in step S21, which iscrossed by the optical spot during the seeking operation.

FIG. 7 shows a speed profile of the optical spot effected by the seekingprocess of FIGS. 5 and 6, while FIG. 8 shows a magnified, detailed speedprofiles effected by the rough actuator and by the fine actuator duringa final stage of the speed profile of FIG. 7. In FIG. 7, during anacceleration period between t0 and t1, the rough actuator 2 acceleratesthe optical head up to the maximum speed Vmax at the maximumacceleration rate. The maximum speed Vmax is set at a speed in thevicinity of the critical maximum speed, for example, 0.5 m/s below whichthe tracking error signal can be effectively detected.

After the travelling speed of the optical spot (or optical head)effected by the rough actuator 2 reaches the maximum speed Vmax, thecontrol section 1 reads out the crossed-track count Nc in step S22 andtravelling speed in step S23, then controls the rough actuator 2 to movethe optical head 4 at a constant speed equal to Vmax before the numberof the remaining tracks (remaining track number: Nt-Nc) becomes equal toa threshold number Nd at t2. The threshold number Nd for remainingtracks can be calculated in FIG. 2 by dividing the area below theprofile between t2 and t3 by the track pitch of the disk file.

When the remaining track number Nt-Nc to be crossed before reaching thetarget track becomes equal to or lower than the threshold Nd in step S24at time instant t2, the control section 1 calculates the travellingspeed of the optical head to be effected by the rough actuator for thesubsequent period, by using equation (4) in step S25. In this way, thespeed of the optical head effected by the rough actuator is decreased.At the same time, the object lens is shifted by the fine actuator 3 withrespect to the optical head to the forward end of the stroke for theobject lens, as viewed in the travelling direction of the optical leadin step S26.

After the travelling speed Vp of the optical head effected by the roughactuator 2 is decreased down to a threshold speed Vr in step S27, thecontrol section 1 maintains the travelling speed of the optical spot atVr in step S29 of FIG. 6. The threshold speed Vr is calculated by takinginto consideration the travel stroke by the rough actuator, accelerationcharacteristic of the rough actuator, and the time period required forread-out of the present address. The threshold speed Vr is generally setbetween 0.05 to 0.1 m/s.

Subsequently, the control section 1 controls the fine actuator 3 to moveand accelerate the object lens in a direction opposite to the travellingdirection of the optical head in step S30, then maintains the travellingspeed of the object lens effected by the fine actuator 3 at -Vr in stepS31, as shown in FIG. 8. As a result, the travelling speed of theoptical spot, which is the relative speed of the object lens withrespect to the disk file, becomes approximately zero, so that thetracking servo system for detecting the present address of the opticalspot can be effectively activated.

During the on-state of the tracking servo system, i.e., during timeperiod between t3 and t4, the control section 1 reads out the presentaddress of the optical spot in step S33, then again calculates a secondcross-track number Nt between the present address obtained in step S33and the target address in step S34. Thereafter, the control section 1calculates the travelling speed for the next time period fordeceleration in steps S35 through S40 based on the second cross-tracknumber Nt.

In detail, the crossed-track count is first reset to zero in step S35,then the cross-track counter starts to count the crossed tracks in stepS36 to obtain a crossed-track count. The fine actuator is moved back tothe center of its stroke in step S37 or at any time. The travellingspeed Vp of the optical spot is then read out. The travelling speed bythe rough actuator for the next stroke is revised based on the equation:##EQU5## in step S39. The remaining track number Nt-Nc is examinedwhether it is zero or not in step S40. If the remaining track numberNt-Nc is not zero in step S40, the process goes back to step S36 torepeat the steps S36 through S40. The cycle of the steps S36 through S40is repeated until the remaining track number Nt-Nc becomes zero. If itis detected that the remaining track number Nt-Nc is zero in step S40,it means that the optical spot is positioned at the target track.Accordingly, the rough actuator is stopped in step S41 and trackingservo system is activated again in step S42 to assure that the presentaddress is the target address, thereby ending the seeking process.

As described above, the travelling speeds effected by the rough actuatorand the fine actuator during time interval t3 and t4 are equal to eachother but in opposite direction, to thereby provide a substantially zerotravelling speed of the optical spot. If the second cross-track numberNt is larger or smaller than the expected remaining track number at thattime, the speed profile to be effected by the rough actuator for thetime interval between t4 and t5 is corrected from the expected profileII in FIG. 8. Accordingly, the travelling speed immediately after thetime instant t5 may be sometimes higher or lower than Vr if the secondcross-track number Nt is larger or smaller than the expected value, asshown by the profile I or III. As a result, only the rough seekingoperation is enough to provide an accurate positioning of the opticalspot to the target track, thereby omitting a fine seeking period and anadditional read-out period for reading the present address, unlike theconventional optical disk drive.

FIGS. 9 and. 10 as combined show a seeking process effected by anoptical disk drive according to a second embodiment of the presentinvention such as shown in FIG. 4, while FIG. 11 shows detailed speedprofiles effected by the rough actuator and fine actuator during thefinal stage of the seeking process of FIGS. 9 and 10. The steps S63through S74 in FIG. 9 are similar to steps S17 through S28 shown in FIG.5, and therefore, the detailed description thereof will be omitted herefor avoiding a duplication. The second seeking process includes a first,acceleration period and a second, constant speed period such as shown inFIG. 7, and a third, deceleration period, as shown in FIG. 11, which isdifferent from that of the first process shown in FIG. 8.

After the travelling speed of the optical head effected by the roughactuator becomes the threshold Vr at t3 in FIG. 11, the control section1 maintains the drive current for driving the rough actuator at thevalue before t3. As a result, the travelling speed is decreased duringthe time interval between t3 and t4 at the constant deceleration rateapproximately equal to the deceleration rate provided thereto before t3.In this state, the control section 1 controls the fine actuator 3 tomove and accelerate the object lens 4A with respect to the optical head4 in the direction opposite to the travelling direction of the opticalhead, thereby reducing the speed of the optical spot relative to thedisk file 14 down to approximately zero.

The reduction in the relative speed is detected by a longer period ofthe tracking error signal. After detection of an enough reduction intravelling speed of the optical spot in step S76, the control section 1activates the tracking servo system to read out the present address ofthe optical spot in step S77. Subsequently, a second cross-track numberNt to be crossed hereinafter is calculated in step S78 based the presentaddress detected in step S77 and the target address. The cross-trackcounter is reset in step S79, and process cycle for revising the speedof the optical head is repeated. In this way, the travelling speeds forthe subsequent time periods are repeatedly calculated based on theremaining track numbers Nt-Nc at the respective time instants in steps80 through 84 similarly to the steps 36 through 40 in FIG. 6.

When it is detected in step S84 that the remaining track number Nt-Nchas become zero, the control section 1 controls the rough actuator 2 tostop the optical head in step S85. The control section 1 activates thetracking servo system to read the present address to assure that thepresent address is the target address, thereby ending the seekingprocess. In this way, the seeking process is completed when the roughactuator is stopped.

In accordance with the process according to the present embodiment, theread-out of the present address is executed during deceleration periodfor the optical head, as shown in FIG. 11. Accordingly, a constant speedperiod need not be interposed between the deceleration periods, unlikethe process according to the first embodiment, so that the totaldeceleration period can be reduced compared to the first seekingprocess.

However, the second process includes the step for making the travellingspeed of the optical spot substantially zero by providing theacceleration to the object lens in accordance with the decelerationeffected to the optical head. This process requires an accuratemechanism for moving the object lens by the fine actuator.

In both the embodiments, the tracking servo system can be effectivelyactivated to read the present address, without stopping the opticalhead, for correcting the speed profile of the optical spot after theread-out of the present address. As a result, an accurate positioning ofthe optical spot can be obtained when the operation of the roughactuator is finished, thereby omitting the fine seeking period andallowing a higher-speed seeking process for the optical spot.

Since above embodiments are described only for examples, the presentinvention is not limited to such embodiments and it will be obvious forthose skilled in the art that various modifications or alterations canbe easily made based on the above embodiments within the scope of thepresent invention.

What is claimed is:
 1. An optical disk drive comprising an optical headfor reading optical data stored along a plurality of tracks of a diskfile, a first actuator for moving said optical head with respect to thedisk file in a radial direction thereof, an object lens, mounted on saidoptical head, for irradiating an optical spot onto the disk file, asecond actuator, mounted on said optical head, for moving said objectlens with respect to said optical head in said radial direction, a speedsensor for detecting a radial speed of said optical spot with respect tothe disk file, an address detector for detecting a present address ofsaid optical spot with respect to the disk file, and a calculatingsection for calculating a speed profile for the optical head based on astroke between a present track before seeking and a target track, saidsecond actuator moving said object lens in the direction opposite to themoving direction of said optical head for controlling the radial speedof said optical spot to thereby generate a stationary state of saidoptical spot with respect to the disk file while said first actuatormoving said optical head between the present track before seeking andthe target track, said address detector being activated to read apresent address during said stationary state of said optical spot, saidcalculating section correcting the calculated speed profile based onsaid present address obtained during said stationary state.
 2. Anoptical disk drive as defined in claim 1 wherein said stationary stateis effected during a constant speed period of said optical head.
 3. Anoptical disk drive as defined in claim 2 wherein said stationary stateof said optical spot is interposed between deceleration periods of theoptical spot.
 4. An optical disk drive as defined in claim 1 whereinsaid stationary state is effected during a deceleration period of saidoptical head.
 5. An optical disk drive as defined in claim 1 whereinsaid second actuator moves, before said stationary state of said opticalspot, said object lens in a forward direction as viewed in the movingdirection of said optical head.